The present invention relates to a timepiece including hands moving above a dial and a date formed of first and second indicators on which figures are affixed indicating respectively the units and tens of said date, this date appearing through a large aperture made in the dial, said date being driven by a date crown-wheel making one revolution in thirty one days at a rate of one step per day, this crown-wheel being arranged to drive the first indicator by one step at the end of every day except at the end of the thirty-first day when it is not driven, and the second indicator at the end of the ninth, nineteenth, twenty ninth and thirty-first day of the month, said first and second indicators each being fitted with a device enabling them to keep a defined angular position when they are not being driven.
A timepiece with a large aperture corresponding to the generic description hereinbefore has already been proposed. This timepiece includes a date crown-wheel arranged to make one revolution in thirty-one days at the rate of one step at the end of each day. This crown-wheel includes two distinct toothings.
A first toothing includes thirty active teeth evenly distributed over a sector occupying the thirty thirty-first parts of the periphery of the crown-wheel so that one thirty-first part of this periphery has no teeth. This first toothing is meshed with a first star wheel carrying a disc on which the date units are affixed. It will be understood that this disc is not driven when the toothless sector of the crown-wheel is in front of the star wheel. This absence of driving is thus arranged to occur between the thirty-first of the month and the first day of the next month. Consequently, the units disc displays the FIG. 1 on two consecutive days, namely the 31 of the month which is ending and the 1 of the month which is beginning.
A second toothing carries four active teeth. This second toothing is meshed with a second star wheel carrying a disc on which the tens of the date are affixed. These four active teeth are arranged on the periphery of the crown-wheel so as to drive this tens disc by one step at the end of the ninth, nineteenth, twenty-ninth and thirty-first days of the month, the tens disc thus displaying respectively 1, 2, 3 and 0.
The units and tens discs are arranged side by side and the figures which they bear appear in a large aperture made in the dial and located on a six-o""clockxe2x80x94midday line of the timepiece. In order to index the figures of each of the discs correctly when they are in their last position, a jumper spring is provided, acting on each of the teeth of the corresponding star wheel, these jumper springs allowing a defined angular position of the discs in question when the system is in its rest position.
Since the diameter of the discs is small, the pressure which the jumper springs exert on the respective star wheels must not be high to keep the discs in place, even in the event of shocks applied to the timepiece.
If, however, one wishes to place the date at three o""clock on the timepiece or around this point (for example between one o""clock and seven o""clock), the construction proposed hereinbefore is not suitable and one has to use at least one indicator of large diameter having the shape of a ring covering a zone located at the periphery of the timepiece, a preferred construction lying in the use of two moving parts of large diameter located concentrically with respect to each other.
In this case, the simple jumper springs proposed hereinbefore, if they properly fulfil the functions expected of them in normal use, are totally insufficient if shocks are applied to the timepiece, since, in such circumstances, the indicators, because of their large size, can move forward or backwards inadvertently and even randomly so that the synchronisation which should exist between these indicators may be broken and no conventional date correction by the stem can correct it. The timepiece then has to be opened to re-establish the lost synchronisation.
In order to overcome this drawback, one could of course increase the pressure exerted by jumper springs on the indicators. However, such measures would have the effect of considerably increasing the torque to be provided by the motor member of the timepiece so that the working autonomy is greatly reduced.
The present invention has found a remedy for this drawback by proposing a system of locks acting on the mechanisms present, these locks consuming no or very little energy while locking the date indicators when they are not being driven normally by the timepiece movement.
To this end, the timepiece of the invention, in addition to answering the definition given hereinbefore in the first paragraph of this description, is characterised in that a first mechanism is inserted between the crown-wheel and the first indicator and that a second mechanism is inserted between the crown-wheel and the second indicator, these first and second mechanisms each being provided with means both rotating the corresponding indicator from the crown-wheel and locking said first and second indicators when they are not being driven by said crown-wheel.
The invention will be described in more detail now relying on the following description, which is illustrated by the annexed drawings given by way of an example of an embodiment, and in which: